Effectiveness of Selected Native Plants as Competitors with Non-indigenous and Invasive Knapweed and Thistle Species

Abstract

Abstract : This work examined the response of native grass populations to long-term presence of non-indigenous invasive plant species (NIPS). Two native grass species common to arid and semi-arid rangelands were identified (alkalai sacaton [Sporobolus airoides] and needle and thread grass [Hesperostipa comata]) as remnants of native communities subjected to NIPS Russian knapweed [Rhaponticum repens]). Maternal grass individuals were collected to examine the influence of the invasions on population genetics and phenology of the two grass species. In controlled greenhouse settings and field plantings, this work examined the growth, seed production, and germination of seedlings of the two grasses in competition with Russian knapweed and NIPS Canada thistle [Cirsium arvense]; and genetic variability of the two grasses via amplified fragment length polymorphism and Inter-Simple Sequence Repeat analyses. Results showed that maternal lines of the grasses demonstrate evidence of natural selection via the presence of the invaders. Continued work was recommended to obtain superior seed sources for native species to target the tradeoffs between phenotypic plasticity and increased vegetative growth, to develop wild seed collection protocols and production techniques so that native plants may be used to restore degraded areas and to reduce the chances of future exotic invasion.